2 HISTORY OF INSECTS. 



increase rapidly in size, and are invariably without wings ; 

 the grubs, when full grown, become for a time motionless ; 

 their skin opens, and from it comes forth the perfect insect, 

 which has four wings, and does not increase in size. In a 

 very great number of insects the grub changes its skin, and 

 completely alters its form, when it becomes motionless; in- 

 deed, almost as great a transformation takes place as on 

 its final change to a perfect insect ; when this is the case, 

 the animal, in its motionless state, is called a chrysalis. 

 Thus we have four stages in the life of an insect, four 

 states which it is necessary thoroughly to understand ; the 

 egg (ovum), which is motionless, and apparently lifeless ; 

 the grub (larva), which is active, but without wings, vora- 

 cious, and grows rapidly ; the chrysalis (pupa], which is 

 quite motionless, and does not occur in all insects; the 

 perfect insect (imago], which is active, has wings, does 

 not grow, and which, by laying eggs, perpetuates its kind. 

 The names egg, larva, pupa, and imago, are the terms 

 generally employed in descriptions ; the three last answer 

 equally well for Latin and English, but it must be borne in 

 mind that the words, grub, maggot and caterpillar, are sy- 

 nonymous with the term larva ; and perfect insect, fly, 

 &c., are synonymous with the term imago; and the English 

 and Latin words are used in English descriptions almost 

 indifferently. These transformations, often spoken of as 

 the metamorphosis of insects, are in reality nothing more 

 than a continual casting of the outer skin ; the larva often 

 casts its skin four or five times, without any very remarkable 

 change of form ; every casting of the skin is a step towards 

 arriving at ultimate perfection. In every insect the skin 

 must be cast a certain number of times, and the last cast- 

 ing brings it to maturity. 



On account of their small size, it is difficult to find com- 

 mon examples of the eggs of insects; those laid on meat by 



